1. Field of the Invention
The present invention relates to a method for dynamically scheduling in a telecommunication service, and especially to a method for dynamic division of the radio capacity in a Time Division Multiple Access (TDMA) system between different packet radio services.
2. Description of Related Art
The global system for mobile communications (GSM) has been disseminated all over the world since 1992. Due to the system complexity, only a limited set of basic speech and circuit-switched data services were specified in phase 1 GSM recommendations. GSM is entered into phase 2+ development on 1996. The major objective of phase 2+ is to build off the huge investments made and prepare GSM for the future mobile telecommunication market by introducing new services.
General packet radio service (GPRS) is one of the new services introduced in the GSM phase 2+ standard. GPRS is designed to support the intermittent and bursty data transfer according to the feature of occasional transmission of the large multimedia data. It uses a packet-mode technique to transfer high-speed (120 kb/s) and low-speed data and signaling over the existing GSM network. Strict separation between the radio subsystem and network subsystem is maintained, allowing the network subsystem to be reused with other radio access technologies by the next mobile communication generation. Applications based on standard data protocols are supported, and internetworking is defined with IP networks and X.25 networks. Specific point-to-point (PTP) and point-to-multipoint multipoint (PTM) services are supported. Four service levels are supported. GPRS, which is compatible with GSM architecture, is designed for the quick reservation of resources to begin the transmission of packets, typically from 0.5 to 1 second. The main idea of the GPRS service is to allocate bandwidth resource on demand. This operating feature is defined as a “capacity on demand mode”.
FIG. 1 shows the protocol stack of the transmission plane for GPRS. The Radio Link Control/Medium Access Control (RLC/MAC) protocol in the GRPS is tailored to the Frequency Shift Modulation (FSM) requirements. Basically, uplink and downlink are independent and asymmetric channel resources. It is necessary to allow Mobile Stations (MSs) to simultaneously transfer packets in both directions in imbalanced data traffic.
The RLC protocol uses a selective ARQ mechanism to handle the retransmission of error RLC/MAC blocks while the MAC protocol uses a slotted-ALOHA-based packet reservation mechanism. A connection is identified as a Temporal Block Flow (TBF). Different QoSs can be achieved by allowing MS to use more than one TDMA time slot in a frame.
[Uplink Data Transfer]
An MS initiates a packet transfer by making a packet channel request on PRACH or RACH. The network responds on PAGCH or AGCH, respectively. The multi-slot channel reservation scheme allows the MS to reserve at least one TDMA time slot in a frame, and thus reduces the transmission delay across the air interference. The bandwidth can be allocated to MSs depending on the number of available PDCHs, the multi-slot capability of the MS, and the current system load, etc.
The BSS sends a 3-bit Uplink State Flag (USF) in all downlink RLC/MAC blocks to indicate which MS can use the next uplink radio block on the same time slot. For example, USF=‘111’ indicates the corresponding uplink radio block containing PRACH, and USF=R1/R2/ . . . /R7 are used to reserve the uplink for different MSs[1].
[Downlink Data Transfer]
A BSS initiates a packet transfer by sending a packet-paging request on the PPCH or PCH downlink. The MS responds to the page by initiating a page response procedure very similar to the packet channel request procedure as mentioned above. Since an identifier named ‘Template Flow Identifier’ (TFI), which is one-to-one corresponding to a TBF, is included in each radio block. The TFI is used to multiplex radio blocks, destined to different MSs on the same PDCH downlink.
In GPRS, several users (or MSs) can share one physical channel (i.e. time slot) and the Base Station (BS) needs a traffic-scheduling algorithm to decide the priority of each MS for transmission its packets based on the requested quality of services (e.g. packet error rate). However, the signal quality received by a Mobile Station (MS) is varied with time in wireless environment and it makes the traffic-scheduling algorithm difficult. Therefore, a proper traffic-scheduling algorithm has to consider about interference region.
The QoS adjustment may be achieved by applying different coding-schemes (e.g. convolution-coding rate 1/2  2/3  3/4 and 1). However, besides the high complexity in MS, the main problem for such a QoS adjustment approach is the long response time required for exchanging the signals due to the negotiating of a new code rate between MS and BS. Also, such a QoS adjustment may not respond to the interference changing pace when an MS moves at high speed.